Recently, there has been an increased interest in biological control techniques using a biological pesticide, which has less environmental load and a higher level of safety for humans and animals compared to chemical pesticides. However, a biological pesticide has a less instantaneous effect and a less therapeutic effect compared to chemical pesticides and can control only a limited range of pathogenic bacteria, and also loses the efficacy of the biological pesticide itself when used in combination with a chemical pesticide. Therefore, the market share of biological pesticides has currently remained only 0.4% of the total market of pesticides.
The technique using a biological pesticide utilizes an organism that is a natural enemy of phytopathogenic microorganisms and pests that cause plant diseases. Bacillus subtilis has been conventionally used as a biological pesticide against the bacteria causing botrytis rot in eggplants, tomatoes, or grapes, since it has antagonistic actions such as growth inhibition and a bactericidal action on phytopathogenic bacteria.
For example, a method for controlling plant diseases which includes a spore fraction prepared from a culture of Bacillus bacteria such as Bacillus subtilis so as to contain 50% or more by weight of spore based on the dry weight is conventionally known as a biological pesticide using Bacillus subtilis (see Patent Literature 1). Furthermore, in order to control plant diseases caused by Phytophthora, a disease control agent is known which includes the bacterial cell or the culture of Bacillus bacteria such as Bacillus licheniformis, and moreover organic acids and salts thereof produced by the bacteria as an active ingredient (see Patent Literature 2).
Furthermore, a plant disease control agent including the bacterial cell or the culture of Bacillus sphaericus is known (see Patent Literature 3), and a plant disease control agent using specific strains of Bacillus subtilis as an active ingredient is also known (see Patent Literatures 4 and 5).
However, the effects of the above-mentioned conventional plant disease control agents in the case of application to a grape are mediated by antagonistic actions by Bacillus bacteria that occupy the nutrition or living area on grape tissues. Therefore, although some preventive effect is produced by spraying prior to the occurrence of diseases, the agents have no therapeutic effect such as a bactericidal action, and thus have been unable to be used after the occurrence of diseases.
Furthermore, the above-mentioned conventional plant disease control agents are effective only for the bacteria causing grape botrytis rot among the pathogenic bacteria of the most common three grape diseases, grape botrytis rot, downy mildew, and ripe rot. Thus, they cannot be expected to have a control effect on the bacteria causing downy mildew and ripe rot other than grape botrytis rot or other pathogenic bacteria for grapes.
Furthermore, although the above-mentioned conventional plant disease control agents settle onto grape leaves, the level of settlement onto pericarps was low. It was also difficult to use a chemical pesticide for safety reasons since grape pericarps are also put into the mouth, and the control of diseases such as botrytis rot and ripe rot, which also occur in fruits, has been difficult.